We have undertaken studies to examine the possible role of protein oxidation and enzyme inactivation in ischemia/reperfusion injury in both heart and brain. Preliminary studies have been carried out with Dr. Robert Floyd, Oklahoma Medical Research Foundation and Dr. John Camey, University of Kentucky using a gerbil brain model of ischemia/reperfusion injury. Initial results indicate that loss of glutamine synthetase activity is correlated with increased carbonyl content during ischemia followed by reperfusion. Although a small amount of protein oxidation is associated with the ischemic event, most of the oxidation occurs during 15 to 60 minutes of reperfusion. It is important to point out that these represent intracellular changes and suggest that both ischemia and reperfusion triggers a cellular response which leads to protein oxidation and loss of enzyme activity. Other studies have been initiated with Dr. Richard Clark and Dr. David DeBoer of the surgery branch of the NHLBI, NIH using a working rat heart model. The initial studies have involved method development. In collaboration with Dr. Moon Bin Yim and Dr. Emily Shacter, we have undertaken additional studies to identify the radicals produced by activated neutrophils under a variety of conditions using electron spin resonance (ESR) and the spin trap, 5.5-di- methyl-l-pyrroline-N-oxide. Although the production of superoxide radical by activated neutrophils has been demonstrated by this method, there are conflicting results with respect to the production of hydroxyl radical by this technique. Again, most of the initial studies have been devoted to method development.